The new line of inquiry suggests the 21-month-old may have been crushed to death by a digger near a farmhouse his grandparents were renovating in July 1991.

Konstantinos Barkas, also known as Dino, was clearing land with an excavator close to where Ben was playing on the day he vanished and may be responsible for his death, a friend of the builder has reportedly told police.

The driver reportedly died of stomach cancer last year, months before detectives from South Yorkshire Police arrived on the island for a renewed investigation.

But Mr Barkas's widow Varvara strongly dismissed any suggestions her late husband had killed Ben in an accident.

A variety of theories on his fate and reported sightings have arisen since his disappearance and Ms Needham had been holding out hope that she would one day be reunited with her son.

South Yorkshire Police have confirmed that its team, led by Detective Superintendent Matt Fenwick, will begin searching a specific site on Kos, starting on Monday. But they warned progress could be painstaking, with the first dig expected to last up to 12 days.

Detectives are said to have carried out initial inquiries at the site, with experts testing soil and surveying the area with drones.

Last week, Mr Fenwick said: "There will be planned operational activity at two locations on the island that have been identified as areas of interest to the investigation.

"We continue to keep an open mind and have updated Ben's family about certain lines of inquiry we're currently exploring."

Earlier this year, South Yorkshire Police received extra funding from the Home Office to help in the search for Ben.

Ms Needham has been forthright in her support of Mr Fenwick's investigation.

In May, she jumped to the defence of the investigation team when they were pictured on the front page of a national newspaper drinking in the sunshine during a visit to Kos.

Mr Fenwick was called back from the island but a lawyer for Ms Needham wrote to the chief constable saying: "Ms Needham trusts the officers involved, believes they are working to the highest standards operationally and professionally and wishes there to be no disruption."